Problem 3.5-2

a.       The resistors in figure P.3.4-2 are in parallel so we have Req given by

1/R_eq = 1/R1 + 1/R2 + 1/R3 = 1/6 + 1/12 + 1/4 = 1/2 so R_eq = 2 Ω.
As the currents are the same in Fig. (a) and (b), then R = 2 Ω makes the 2 circuits equivalent.

b.      The voltage is U = R*I = 2*6= 12 V

c.       The power supplied by the source is P = U*I = 12*6 = 72 W